Audi Q8 AC Failure: Compressor Issues & Quick Fixes

Had this exact same issue with my 2020 Audi Q7 last summer, and I have some experience working on basic car maintenance. The symptoms match perfectly, no cooling and complete HVAC system shutdown. In my case, it was an undervoltage problem affecting the A/C compressor and AC relay. The pressure switch was getting incorrect voltage readings, causing the system to shut down as a safety measure. Took it to a workshop where they diagnosed the electrical system. They found and fixed a faulty belt tensioner that was causing inconsistent power delivery to the A/C components. Total repair cost was 240 Euro, including parts and labor. Before you head to the shop, could you share: Does the fan blow at all, just without cold air? Are you hearing any unusual sounds when trying to activate the AC? Have you noticed any other electrical issues like dimming lights? What is the exact fault code showing? This info would help determine if youre facing the same underlying issue. The Q8s HVAC system is very similar to the Q7, so troubleshooting steps should be comparable.

Exactly right about the HVAC system problems. My mileage is at 145280 KM and the fan does blow but without any cooling effect. No unusual sounds when activating the air conditioning, and the fault code reads P0531. After checking the workshop manual, the pressure sensor seems to be reading out of range values. No issues with dimming lights or other electrical problems, which makes me think its not a belt tensioner issue like in your case. The refrigerant leak test at my last service showed normal pressure, so Im leaning towards an electrical issue with the sensor itself rather than a mechanical problem with the compressor.

Thanks for those details, this sounds different from my Q7 case since youre not experiencing any electrical symptoms. The P0531 code usually points to an A/C refrigerant pressure sensor circuit issue, rather than the belt tensioner problem I had. Given that your refrigerant levels tested fine and theres no odd noises from the A/C compressor, Id focus on the sensor circuit. The HVAC system likely isnt activating the compressor because its getting incorrect pressure readings. In my Q7, after the belt tensioner fix, I actually had a similar sensor issue about 6 months later. The pressure sensor wiring had some corrosion at the connector, causing intermittent communication problems. The repair involved cleaning the connector and replacing the sensor, cost was around 180 Euro. Some checks before a shop visit: Look for visible damage to wiring near the A/C compressor, Check if sensor connector is properly seated, Monitor if the issue gets worse in wet weather Since the refrigerant leak test was good and theres no mechanical symptoms, this looks more like a sensor circuit problem than a major A/C system failure.

Thanks for the detailed input. You are absolutely right about checking the sensor circuit first, that makes a lot of sense given the P0531 code and the fact that the air conditioning system shows no other concerning symptoms. I checked the wiring as suggested and found some signs of wear near the pressure switch connector. The connection does seem a bit loose, which could explain the irregular sensor readings causing the A/C system to shut down. This definitely aligns with your experience regarding connector issues. I will try cleaning the connector first and make sure its properly seated. If that doesnt resolve the problem, I will have the pressure switch replaced since its likely the root cause rather than a refrigerant leak or compressor issue. Really helpful to know the repair cost was reasonable in your case at 180 Euro. Will schedule an appointment with my regular shop but at least now I have a better idea of what to expect. Good to rule out the more expensive A/C compressor problems before going in.